After briefing the senior officers on the nature of the problem, Pran and most of the other officers leave the observation lounge, leaving Data alone with Juliana Tainer. Juliana asks Data if he remembers her, and when he says he does not, she reveals she was Dr. Noonian Soong's wife, and involved in Data's construction, making her Data's mother.

In Ten Forward, Data and Juliana sit down to talk. Juliana reveals details of Data's early days, which she considers to be his childhood. Data had trouble with his motor skills and sensory processing at first, and Dr. Soong tinkered with his programming until he'd corrected the problems. At this point, the Soongs deactivated Data, wiped his memory, and gave him the experiences and logs of the Omicron Theta colonists in an effort to develop Data's Humanity without the aid of emotions. It was during this time that the Crystalline Entity attacked the colony, and the Soongs were forced to flee. Juliana explains that the life pod in which she and Dr. Soong escaped only had room for two, and they had to leave Data behind.

Data is curious as to why, when he met Dr. Soong on Terlina III, Soong did not mention Juliana, and why there was no record in the colonists' logs of Soong's marriage to Juliana. Juliana tells Data the story of how she and Soong eloped on Mavala IV because Juliana's mother disapproved of Soong's occupation. It wasn't her dream wedding, but Noonian had a way of making the oddest things seem romantic. When Data agrees that his father had an unusual way of looking at things, Juliana is pleasantly surprised to find out that Data had met him, but then is shocked when Data states that he died soon after. She had no idea that he was dead and admits the news has hit her harder than she thought it would, as they had not parted on the best of terms. Then Juliana tells Data that she eventually left Soong because he was more focused on his work than her, and their solitary life in the jungle of Terlina III was "no life at all." Keen to get to know him better, Juliana suggests they spend more time together, but Data brusquely tells her that he wants to corroborate her story first.

Data joins Geordi La Forge in engineering, and proceeds with verifying what Juliana told him. He finds records that show Soong and Juliana spent four days on Mavala IV, but there is no accompanying proof of marriage. La Forge suggests that Data is looking for a lie, but Data protests that he merely can't figure out why Soong would never have mentioned his wife. Aware of the fact that Juliana left Dr. Soong, La Forge wonders if maybe Soong had his heart broken and wasn't eager to discuss the experience. Together, he and Data surmise that there may be hidden memories inside Data's emotion chip about his mother, which Soong intended Data to access when he was ready.

Data is still clearly confused by the situation, and La Forge notes that it's because it doesn't fit in Data's logical processors – there's no rational explanation. This, La Forge says, is life, and Data needs to get used to life not conforming to his preconceptions. Disturbed by a past he cannot remember, Data nevertheless says he's curious to know more about his mother.

As Juliana and Data walk through the halls, Juliana mentions that she had wanted a daughter while Soong had wanted a son. The dispute was settled when Soong created Data's head in his own image. When Juliana and Data reach CounselorTroi's quarters, Juliana remarks that Soong would be relieved to see that Data's sexuality program was fully-functional. As Data attempts to correct her, Juliana bids him goodnight and walks away with a teasing smile.

The next day in engineering, Data, La Forge and Juliana are getting ready as the ship moves to establish synchronous orbit over the drilling site. When Data thanks La Forge for reconfiguring the phasers, Juliana giggles, pleased with Data's manners; it wasn't easy to strike the right balance with his programming. She explains that Data didn't care about being polite and was in fact downright rude, something La Forge can't quite imagine. She continues on for a moment then stops, not wanting to embarrass Data in front of Geordi, but he reminds her that's not possible for him and asks her to go on. She reveals that one thing she and Soong couldn't possibly have anticipated was that Data didn't mind being naked, although some of the colonists certainly did as he is anatomically correct. The Soongs asked him to dress, but he didn't feel it was necessary as he didn't "suffer from the elements." With a laugh, Juliana concludes that they had to resort to writing a modesty subroutine just to keep his clothes on.

From the bridge, CommanderRiker lets them know the Enterprise is in position. On overhearing Data's calculation for the phaser burst, after Riker acknowledges, Pran asks Riker if someone double checked Data's calculations, as he assumes that they would regularly do so. Riker states that they didn't but is sure that Data knows what he's doing; when Pran says that they should as Data is a machine, Riker remains professional and states his complete confidence in Data's "ability to check up on himself" and goes ahead with the drilling. It goes off without a hitch and Riker congratulates Data, saying he doesn't think it could have gone any better while giving Pran a meaningful sidelong glance. As Juliana also gives credit to Data's work and that she couldn't have done it without him, Pran keeps silent, his beliefs about Data having been proven unfounded. With several hours to wait before they can continue and Data having free time, Juliana suggests they spend some time together and asks to see his quarters.

In Data's quarters, Data plays a Handelviolinpiece for his mother, telling her that he will play the piece at a recital the next evening. Juliana says that Data's performance was beautiful, causing Data to wonder if she is exaggerating his abilities as most parents do of their children. Juliana also reveals that she was responsible for Data's creative aspect, a part of his programming which Dr. Soong considered irrelevant in the absence of emotion. Data confides in his mother that it is during his creative endeavors that he feels that he comes closest to Humanity. After saying that she's quite familiar with the Handel piece, Juliana offers to accompany Data on the viola at the recital next evening.

Data replicates a viola for her with which they can practice for the recital; she chuckles softly when he says "please" to the computer. She then notices Data's paintings, including one of his late daughter, Lal. When Data supplies the story of her inception and subsequent deactivation, Juliana looks slightly shaken. Data is unperturbed and asks if she would like to go practice. After practicing in Ten Forward, Juliana asks Data if he will ever try creating another child. Data still wishes to procreate, but Juliana begins recounting the difficulties she and Dr. Soong encountered. She relates to Data that she and Dr. Soong had created and lost three prototypes prior to Lore, and that Lore's cruel and evil nature had almost convinced them to stop trying. In fact, Juliana had cautioned against creating Data.

This causes Juliana to reveal the reason that she had avoided contact with Data after realizing he'd survived the attack on Omicron Theta: guilt. She had deliberately left Data behind when she could have taken him with her and Dr. Soong in the life pod. She feared at the time that Data would eventually become like Lore, and forced Soong to abandon him when the Crystalline Entity came. Before Data can react, Juliana rushes out of the room in tears.

Drilling continues on the surface of the planet, with Data, La Forge and Dr. Tainer once again working from engineering. Suddenly the ship rocks: feedback pulses are picking up along the particle beam. Dr. Tainer believes the phaser beam must of impacted a pocket of magnesite ore, and tries adjusting the phaser harmonics to compensate for the pulse. Riker calls down, saying that they will have to terminate the beam if the feedback keeps up. Data explains that if they do, they would have restart the process in another suitable location; Dr. Tainer states that there are no other locations and asks for a few more seconds. La Forge starts to say that it will take her a lot longer than they have, but she unexpectedly finds the right frequency and the feedback ends. Dr. Tainer just attributes it to luck, but doesn't notice Data giving her a long, pondering look. The Tainers and Data beam down to the first magma pocket to set up the infusion unit.

Later, as they are working in the magma pocket, Data notices something particular about Dr. Tainer's face. Pran Tainer then admits to Data that Dr. Tainer told him what she told Data. He begins to say that he understands if Data was angry with his wife, however Data explains that he has no emotions. Juliana confirms Data's question that had Data been a biological child, she would not have left him behind. However, when Data asks if that meant that she values biological life over artifical life, she adds, in an emotionaly stung tone that it did not make it any easier. It had hurt every time she and Dr. Soong lost one of Lore's predecessors, and even shutting down Lore, although necessary, had taken a severe emotional toll on her. She was just afraid of how Data would turn out; if he had become another Lore, they would have had to shut him down too, and losing Data was something she was certain that she wouldn't be able to take yet again. She is not trying to justify leaving Data behind: she's just sorry that she did and hopes he believes her. Now knowing the truth, Data tells her that he understands and sharing a nod with Pran, who appears gratified that the matter has been resolved, they get back to work.

In the evening, Data and Dr. Tainer perform the recital in Ten Forward. The performance goes perfectly, a fact that Data, in the middle of their playing, seems to suddenly notice of Juliana.

Data apparently asks to talk with Dr. Crusher immediately after in sickbay, as she was attending the recital and they walk in with him still carrying his violin. Data wants to see Dr. Tainer's medical records and see if there is anything wrong from her transporter trace pattern, for reasons he says that he does not want to specify but states that he does have a good reason. Dr. Crusher is initially reticent, but likely relents because Data is considered a close relative. She replies, after looking at Dr. Tainer's records, that Juliana only seems to have a mild case of hypertension, a normal occurrence for her age. When she asks Data once more, he only says that he believes that Dr. Tainer may not be who she claims to be. Commander Riker calls Data at this point, reporting a cave in in one of the magma pockets and they need him in Transporter Room 2.

Data is informed that one of the magma pockets has become unstable. Pran and an assistant were doing a final check of the infusion units when one of the walls gave way; Pran sustained some injuries. La Forge reports that its stable for the moment but seismic stress is building and at most, they have about 12 hours before the pocket collapses. The Tainers decide that they must finish configuring the remaining infusion unit and inject the plasma immediately. Riker is hesitant to send anyone inside, but the Tainers insist: it could take months to find another site, time they just don't have and he agrees, as long they finish quickly. Juliana goes in Pran's place.

Dr. Tainer and Data proceed to be transported into the pocket. After Data rearranges the pattern enhancers they make their way through the now treacherous pocket to get to the infusion unit. The unit was damaged, and they must restart the programming sequence. Riker soon checks with them, informing them of an increase in seismic stress. Data promises to expedite their work, and they quickly wrap up, finish the recalibration and bring the unit online. As they proceed to the transport point however, they realize that it has sunk far below their current level due to the seismic activity. Data determines that since there is no way to climb down, they will have to jump. Dr. Tainer protests, fearing that it is too high, but there is not enough time. Data takes her down with him. But while he easily lands on his feet, he sees that Dr. Tainer's arm has been separated from her collapsed body at the shoulder – and circuitry flashes within it.

In sickbay, La Forge examines the circuitry present in Dr. Tainer's head as Dr. Crusher scans her. It becomes apparent that Juliana Tainer is an Soong-type android, one more advanced than Data. Her internal machinery was designed to give off Humanlife signs. Dr. Crusher, however, is puzzled as to why she deactivated upon sustaining her injuries: as far as she can see, she should be conscience. Data suggests checking for a cascade anomaly in her positronic matrix. He clarifies to Riker that he had already worked out that she was an android, picking up on a few cues that were too subtle to be noticed by anyone other than him. During the feedback pulse incident, he reveals he saw her perform complex calculations without the computer's help: he agrees with Riker that it could have just meant she was good at math, but it was enough to get his attention. He later noticed in the magma pocket that her blinking is actually a pattern that is governed by the Fourier series mathematical formula that Soong had used for him to give the appearance of randomness, and she repeated the exact same performance from their private rehearsal, something impossible for a human to do. Upon examining her further, La Forge finds an information chip built with a holographic interface.

A hologram of Dr. Soong talks to Data about his "mother" on the holodeck.

Data activates the chip in the holodeck, and a hologram of his father, a graying Noonian Soong, appears, explaining that he would answer any questions as to the nature of the Juliana android. When Data identifies himself, Dr. Soong becomes pleased; he hoped Data would be the one to activate the hologram, and wrote a special response program for him. Dr. Soong explains that Juliana was severely injured in the Crystalline Entity's attack on Omicron Theta, and by the time they had gotten as far as Terlina III, fell into a coma. Once he knew she would never come out of it, he built an android and strove to perfect his synaptic scanning technique to encode a person's memories into a positronic matrix, so that he could somehow salvage her consciousness. He wasn't sure that it would work but he had to try, unable to stand the thought of losing the only woman he had ever loved. A few days after the real Juliana Soong died, he activated the Juliana android, complete with experiences and memory; the hologram shows the elation Noonian felt with how he had succeeded, but then his face soon falls. They were happy, but Dr. Soong's failure to adequately express his love for Juliana prompted her to leave him, something, he notes, that the original would have done too. He designed her to shutdown if the truth was discovered, and all Data needs to do is to put back the information chip and make up some excuse, as she will remember nothing. Data asks why he didn't tell her what she was, but Noonian says that there was no need: he wanted her to be happy, and in every way that mattered she was Juliana Soong. In the end, Dr. Soong sternly admonishes his son not to tell her that she is an android, so that until her body automatically shuts down after a long life, she can live out the rest of her life as a Human. He pleads with Data to not take her Humanity from her.

Data is confronted with a difficult choice, and consults with Counselor Troi, Dr. Crusher, and CaptainJean-Luc Picard in the observation lounge. He understands his father's motives that he felt she'd wouldn't be happy if she knew the truth, but feels that his father's wishes are not necessarily the most important, as Data is more concerned with Juliana's best interests. Dr. Crusher opines that she may be better off knowing the whole truth about herself, but Troi points out that she has believed herself to be Human all this time and the truth might be devastating. Picard ponders that there could be another situation in the future where the secret could be exposed anyway: perhaps she should learn the truth from him now. Dr. Crusher adds that if it were her, she would want Wesley to be the one to tell her. However, Data admits that he is having difficulty separating what would be best for her from what would be best for himself. He wants to tell her the truth and not be the only one of his kind in the universe; they'd have something in common to share. Troi says that she understands, but states that if he did tell her, he would be taking away the one thing he himself has strived for all his life: being Human. Nevertheless, Captain Picard reassures Data that they will support whatever decision he comes up with.

Data replaces the information chip in Dr. Tainer's head, and just like Dr. Soong related with her activation, she comes to, looks up and Data and smiles. As programmed, the last thing she remembers is the jump. Data tells her she lost consciousness and broke a bone in her arm from the fall, but Dr. Crusher repaired it and that everything is fine. While factually accurate, Data's description is also entirely consistent with human injuries.

As Juliana Tainer prepares to be transported off the ship, Data relates that Dr. Soong had told him that he had only one great love in his life, and that he regretted not telling her how much he cared for her. Data says that he "is certain" his father was talking about her, to cover the fact that the Soong hologram directly confirmed it. Juliana is clearly moved, grateful for the knowledge. Juliana replies that she is consequently not surprised that Data developed and turned out so well – as the Atreans would say, he is the natural outcome of two parents who loved each other. Juliana bids her son farewell, asking him to take care of himself and Data tells her goodbye, calling her Mother as he does so.